ICE SLURRY PRODUCTION IN A TUBULAR HEAT EXCHANGER

International audienceOne of the challenges of ice slurry generation using a heat exchanger is to overcome the risk of choking. The nucleation usually appears after a supercooling state that remains a key aspect of this technology. In order to focus on this crucial problem, the crystallization of a water ethanol solution was studied in a transparent tubular heat exchanger. Our experiments consisted in cooling the solution until ice slurry formation. Flow visualization permitted mainly to determine the conditions of crystallization according to the flow rate. A limited range of flow rate permitted to obtain the desired ice slurry quality. The heterogeneous crystallization appeared on the wall and dendrites began to develop before being carried away by the solution. Experiments also indicated that dendrites growth from the freezing front upstream in the counter flow direction. The velocity of this retro-propagation phenomenon was estimated using an image analysis tool. Temperature measurements also provided important information on this retro-propagation. Selected process parameters have to be properly adjusted (flow rate, wall properties …). This technology has been patented by the CNRS in selected European countries and in the USA

Analysis of the drying kinetics and the energy efficiency of the ElectroHydroDynamic (EHD) drying of Mushroom Slices

International audienceSeveral recent studies have investigated alternative techniques in order to enhance heat and mass transfer in food processes and to reduce their energy consumption. This is particularly true for the drying process which is a very energy-intensive process. One of the most promising alternatives consists in combining low velocity convection with ElectroHydroDynamic (EHD) enhancement by corona wind. An electric wind is generated by electrodes and leads to secondary flows that may improve the surface heat and mass exchanges. In this study, the drying kinetics of mushroom slices and the energy efficiency of the drying process were analyzed for different EHD conditions. Air was blown in a tunnel (15×15×190 cm) at 45°C 10% RH at two different primary air velocities (0.4 and 2.2 m/s). Mushrooms were placed on a grounded perforated plate. The ionic wind was generated by a wire electrode suspended horizontally at 6 cm above the mushrooms (Figure 1). Experiments were conducted during 5 hours with four levels of applied voltage at the electrode (0, 20, 25 and 30 kV). During drying, the voltage and current of the EHD system, the weight changes of mushroom slices over time were recorded. We investigated drying rates, final moisture content and energy consumption of the EHD system, of the convective system and of the combined process. The energy analysis of the convective system was based on the modelling of the air handling unit. Results indicated that the combination of 30 kV voltage with the air velocity of 0.4 m/s could significantly increase the drying rate. However, a cross-flow with the high velocity of 2.2 m/s diminished the effect of corona wind. As expected, the total energy consumption is greatly affected by the primary air velocity. The combination of low air velocity and high electric field intensity shows the potential for industrial applications. Figure 1: sketch of the experimental setu

Sainte Thérèse de Jésus : conférences données a l¿ocassion du cinquantenaire de la Restauration du Couvent des Carmes déchaussés de Bruxelles

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2012-2013En imprimatur consta 191

ANALYSIS OF THE ENERGETIC AND EXERGETIC EFFICIENCY OF THE ELECTROHYDRODYNAMIC DRYING PROCESS

International audienceDrying is an energy intensive unit operation encountered in many industrial sectors, especially in the food industry. Still over 85% of industrial dryers are convective type. Electrohydrodynamic convective drying (EHD drying) is a novel drying method used to enhance forced convection drying by using electrodes to create an electrostatic field and generate an electric wind. This latter may alter the boundary layer and enhance the heat and mass transfer. In this study, experiments were performed to analyze the drying kinetics during EHD and forced convection (FC) drying experiments. Transient energy and exergy efficiencies expressions were discussed, proposed and computed for each experiment. With airflow of 0.3 m/s in the case of EHD configurations, similar drying rates than FC at 1.0-2.0 m/s can be achieved. Moreover, it leaded to greater energy efficiency (x5) and it was confirmed, using exergy efficiency concept, that EHD better used energy than FC

PHASE CHANGE UNDER STATIC ELECTRICAL FIELD; IN THE CASE OF LIPIDS

International audiencePhase change in biological tissues may be affected by electrical and magnetic disturbances. Freezing under static electric field of water, aqueous solution and pork meat has been investigated by the authors, showing the ability of this process to refine ice crystals in frozen matrices. SEF affects the supercooling, which is usually reduced with SEF. SEF also triggers the nucleation. The use of radiofrequencies and microwaves has also been used recently by researchers to promote refined ice crystallization in food systems. A focus is proposed on recent experiments done on solidification of a vegetable fat mix (Vegetaline ® – France) under static electric field (SEF). Results showed that SEF affects the supercooling and the phase change temperature of the fat mix indicating a possible impact on the crystalline structure of the solidified fat

Ohmic heating applied to the baking process: experimental and numerical approaches

International audienceThis work aims at studying the feasibility of ohmic heating (OH) technology applied to the baking process. The method includes proofing (fermentation) and baking and leads to the production of crustless sandwich bread without the need of cutting the crust away, in a shorter time and with theoretically lower energy costs than conventional baking. An ohmic cell was made to study the electrical conductivity (EC) of bread dough under different experimental conditions. The results showed that the EC increased linearly with the temperature, except during the starch gelatinization stage (60 – 76 °C) because of the bounding of water. The EC decreased with the porosity of the dough when fermented by yeasts, and drastically decreased with the reduction of salt content in the dough, showing the need to control the product formulation. An ohmic baking oven monitored by a PLC was developed to perform both proofing and baking in the same apparatus. The results showed that using OH to quickly reach the optimal temperature of yeast activity (35 °C) significantly reduced the lag phase and shortened the total proofing time. A numerical model was developed and validated by experimental results, taking into account heat and water (vapour and liquid water) transfers. The results confirmed the importance of temperature gradients between the surface of the electrodes and the core of the product, first observed by the underbaked aspect of the bread loaf on its sides. Different baking scenarios and their impacts on temperature and water content gradients were modelled

Grabbing Olives on Linear Pizzas and Pissaladières

International audienceIn this paper we revisit the problem entitled Sharing a Pizza stated by P. Winkler by considering a new puzzle called Sharing a Pissaladiere. The game is played by two polite coatis Alice and Bob who share a pissaladière (a p × q grid) which is divided into rectangular slices. Alice starts in a corner and then the coatis alternate removing a remaining slice adjacent to at most two other slices. On some slices there are precious olives of Nice and the aim of each coati is to grab the maximum number of olives. We first study the particular case of 1 × n grid (i.e. a path) where the game is a graph grabbing game known as Sharing a linear pizza. In that case each player can take only an end vertex of the remaining path. These problems are particular cases of a new class of games called d-degenerate games played on a graph with non negative weights assigned to the vertices with the rule that coatis alternatively take a vertex of degree at most d. Our main results are the following. We give optimal strategies for paths (linear pizzas) with no two adjacent weighty vertices. We also give a recurrence formula to compute the gains which depend only on the parity of n and of the respective parities of weighty vertices with a complexity in O(h 2) where h denotes the number of parity changes in the weighty vertices. When the weights are only {0, 1} we reduce the computation of the average number of olives collected by each player to a word counting problem. We solve Sharing a pissaladière with {0, 1} weights, when there is one olive or 2 olives. In that case Alice (resp. Bob) grabs almost all the olives if the number of vertices of the grid n = p × q is odd (resp. even). We prove that for a 2 × q grid with a fixed number k of olives Bob grabs at least k−1 3 olives and almost always grabs all the k olives

Grabbing olives on linear pizzas and pissaladières

In this paper we revisit the problem entitled SHARING A PIZZA stated by P. Winkler by considering a new puzzle called SHARING A PISSALADIERE. The game is played by two polite coatis Alice and Bob who share a pissaladière (a p × q grid) which is divided into rectangular slices. Alice starts in a corner and then the coatis alternate removing a remaining slice adjacent to at most two other slices. On some slices there are precious olives of Nice and the aim of each coati is to grab the maximum number of olives. We first study the particular case of 1 × n grid (i.e. a path) where the game is a graph grabbing game known as SHARING A LINEAR PIZZA. In that case each player can take only an end vertex of the remaining path. These problems are particular cases of a new class of games called d-degenerate games played on a graph with non negative weights assigned to the vertices with the rule that coatis alternatively take a vertex of degree at most d. Our main results are the following. We give optimal strategies for paths (linear pizzas) with no two adjacent weighty vertices. We also give a recurrence formula to compute the gains which depend only on the parity of n and of the respective parities of weighty vertices with a complexity in O(h 2) where h denotes the number of parity changes in the weighty vertices. When the weights are only {0, 1} we reduce the computation of the average number of olives collected by each player to a word counting problem. We solve SHARING PISSALADI ÈRE with {0, 1} weights, when there is one olive or 2 olives. In that case Alice (resp. Bob) grabs almost all the olives if the number of vertices of the grid n = p × q is odd (resp. even). We prove that for a 2 × q grid with a fixed number k of olives Bob grabs at least k−

Détermination de la répartition spatiale optimale des sources thermiques dans un plateau chauffant

International audienceDans ce travail, on s'intéresse à l'optimisation du chauffage d'un outillage (plateau chauffant) utilisé dans la mise en forme de matériaux composites à hautes températures (~400°C). L'objectif recherché est d'assurer la maîtrise du champ de température en tout point à la surface de l'outillage qui doit reproduire un champ consigne donné afin de chauffer un moule ayant une forme complexe. Pour ce faire, une procédure a été mise en place afin de déterminer la répartition spatiale optimale des sources thermiques de chauffage. La démarche proposée comporte deux étapes : (i) la définition d'une courbe paramétrée qui définit la répartition spatiale des sources de chauffage dans l'épaisseur du plateau chauffant et (ii) l'utilisation d'une méthode inverse couplant un algorithme d'optimisation stochastique avec un code de calcul par éléments finis. Cette deuxième étape permet d'ajuster cette courbe afin d'obtenir un champ de température simulé le plus proche possible de celui voulu à la surface du plateau. On étudie l'évolution de cet écart entre les champs de température ainsi que la consommation énergétique en fonction du nombre de sources retenu. Nomenclature (11 points, 2 colonnes) H Hauteur (m) Valeur maximale de (°C) L Largeur (m) Température normalisée entre [0,1] et Paramètres de la courbe à optimiser Courbe paramétrée Température consigne (°C) Ecart quadratique moyen (°C) Valeur minimale de (°C

Congélation de produits alimentaires : amélioration de la cristallisation par applications de micro-ondes

National audienceLa qualité d'un produit congelé est liée à la cristallisation ; en règle générale, plus la taille des cristaux de glace est petite, meilleure sera la qualité du produit. Un procédé innovant a été évalué dans le cadre du projet européen (FREEZEWAVE). Une assistance micro-ondes (2450 MHz) a été utilisée pour perturber le changement d'état de l'eau. Sur un prototype de laboratoire, les expériences ont confirmé que, quels que soient le mode d'application des micro-ondes et les paramètres du procédé, on observe une réduction de la taille des cristaux. Cet impact positif a été obtenu sur diverses matrices alimentaires, dont des pommes de terre. Un modèle de prédiction a par ailleurs permis de qualifier ces cinétiques. Deux concepts sont avancés pour expliquer ces effets bénéfiques. Abstract FREEZEWAVE project (SUSFOOD ERA-net project 2015-2018